The isolation of individual colonies of micro-organisms (and in particular bacteria) is an important procedure in many microbiological laboratories. Traditionally, this isolation of bacteria has been performed manually by skilled laboratory technicians who first dispense a microbiological sample onto the surface of a solid growth culture medium, such as agar in a Petri dish (which will hereafter simply be referred to as a “medium” in an “agar plate” or simply in a “plate”), followed by the use of a hand-tool to spread the sample across the surface of the medium (called “streaking”).
The hand-tool typically includes a terminal loop to make multiple streaks of increasing dilution of the inoculum across the medium. The streaks of increasing dilution tend to provide, generally towards the tail of the streaks, a number of single cells that allow for the growth of isolated microbiological colonies after incubation. These isolated colonies may then be analysed for colony morphology, and may undergo staining and other procedures which are necessary for determining, for example, the genus, the species and the strain of the previously unidentified organism.
Such inoculation and streaking is highly repetitious and in many pathology diagnostic microbiology laboratories is usually conducted in very high volumes, such as in volumes as high as 1,000 to 15,000 plates per day. It is tedious and laborious work that therefore is prone to error and inaccuracies. It is quite obviously work that would lend itself to either partial or full automation.
The literature is replete with suggestions for how best to automate these laboratory functions, yet very few of these suggestions have ever actually found success in a commercial laboratory environment. It therefore appears that the successful enablement of suitable laboratory apparatus has to date, for most, proved elusive.
Three recent suggestions for the automation of these laboratory functions can be found in the following documents; U.S. Pat. No. 4,981,802 (C. Wylie et al) titled “Method and Apparatus for Streaking a Culture Medium”, U.S. Pat. No. 6,617,146 (F. Naccarato et al) titled “Method and Apparatus for Automatically Inoculating Culture Media With Bacterial Specimens From Specimen Containers”, and international patent publication WO2005/071055 (Medvet Science Pty Ltd) titled “Microbial Streaking Device” (licensed to the present applicant).
The Wylie and Naccarato patents describe automated and semi-automated apparatus that utilize re-usable streaking tools similar to the hand streaking tools mentioned above, without describing a suitable system or mechanism for that apparatus to determine, in three dimensional space, the precise location of the surface of the medium.
While the Medvet Science publication describes the use of a new form of streaking tool, being a streaking applicator that includes a line of spaced apart contact surfaces (for contact with the surface of solid growth media), the contact surfaces being resiliently flexibly supported by a common support member, this new streaking tool still of course requires placement upon the surface of the medium. The Medvet Science publication suggests that this can be dealt with providing the apparatus with a pressure sensing device to determine when the tool is suitably upon the surface.
It will be appreciated that the height of medium, such as agar, within a plate will fluctuate depending upon many factors. For example, not only do different plate and solid growth culture medium suppliers invariably produce agar plates, for example, with a wide variety of surface heights from one supplier to the next, but even the same suppliers tend to supply their own plates with varying heights of media. Also, different compositions and ages of media used for this purpose tend also to produce plates with different media surface heights. Therefore, and due to such fluctuations in height, it is generally not possible for an automated streaking apparatus to rely upon the height of the surface of media in all plates to be the same.
It is therefore not feasible for an inoculating device, for example, of such an automated apparatus to rely on being able to place inoculum upon the surface of media at the same location in three dimensional space for every plate to be processed thereby, and significant difficulties and complexities can be introduced in an apparatus that does. As another example, there are also potential difficulties and complexities for a streaking device of such an automated apparatus in trying to place a streaking tool upon the surface (so as to spread the inoculum rather than to gouge the surface) of media at the same location for every plate in three dimensional space.
In relation to an inoculating device, it will be appreciated that the incorrect location of a dispensing tip in the z dimension (height) will give rise to the inoculum being dispensed from too high (and thus not dispensing as required), or there being contact with the surface such that the tip gouges the surface of the medium. In relation to a streaking device, incorrect location of the contact surfaces in the z dimension (height) will give rise to there either being no contact with the inoculum whatsoever, or there being too much contact such that the streaking tool also gouges tracks in the surface of the medium.
It is an aim of the present invention to provide both a method and an apparatus capable of locating the surface of the medium in a plate prior to, for example, inoculation and streaking of that plate. In this respect, and as foreshadowed above, it is also an aim of the present invention for the method and apparatus to find use in laboratory situations other than the inoculation and streaking situations described above. Indeed, the method and apparatus of the present invention may find use in any laboratory to simply provide a process, for any purpose, for locating the surface of solid growth culture medium in a plate.
Before turning to a summary of the present invention, it must be appreciated that the above description of the prior art has been provided merely as background to explain the context of the invention. It is not to be taken as an admission that any of the material referred to was published or known, or was a part of the common general knowledge in Australia or elsewhere.
It is also useful to provide an explanation of some of the terms that will be used to define the spatial relationship of the apparatus and various parts thereof. In this respect, spatial references throughout this specification will generally be based upon a plate ultimately being inoculated and streaked in an automated streaking apparatus in an upright orientation, with the surface of the medium in the plate being generally flat and horizontal. With this environment as the basis, the apparatus and some parts thereof may then be defined with reference to the “horizontal”, allowing further references to “upper” or “upwardly” and “lower” or “downwardly”, and also to the “vertical”. In this respect, the traditional geometric spatial reference to x, y and z dimensions, and then to the x direction (or axis), the y direction (or axis) and the z direction (or axis), will also be adopted, with the x and y directions lying generally horizontally and the z direction lying generally vertically.
Finally, some aspects of the present invention that may ultimately be claimed in isolation (and not in an in-use environment), may nonetheless be difficult to describe and understand in isolation. Thus, some of the following description does describe the invention and its embodiments in such an in-use environment (for example, in association with a plate carrying medium within an automated streaking apparatus). Of course, it must be appreciated that the use of such description, and the use of the abovementioned spatial relationships, to define the present invention, is not to be seen as a limitation and certainly is not to be seen as a limitation only to the in-use environment, unless that intention is clearly stated.